Digital Mobile Radio (DMR) protocol is a new type of communication protocol adapted for digital trunking communication system, which adopts the two-timeslot TDMA (Time Divide Multi Address) structure. As shown in FIG. 1, each burst sequence includes two timeslots, where each timeslot is 30 ms and each burst sequence is 60 ms. The objective of this protocol is to realize two calls via two timeslots in 12.5 KHz bandwidth; thus the channel efficiency of 6.25 KHz bandwidth can be realized.
DMR protocol includes direct mode (i.e., transmitting without repeater) and repeating mode. In one operating mode of the direct mode, a radio in transmitting state may only use one timeslot to realize a call. The other operating mode is channel inversion mode. As shown in FIG. 2, in channel inversion mode, radio MS2 which is receiving in timeslot 1, may send back in timeslot 2 a reversing burst signaling to the radio MS1 which is in transmitting state. The reversing burst (designated by the slashed part in FIG. 2) is a relatively short frame, which cannot be used to transmit audio signal, and can only carry the status data to notify the radio in transmitting state of the current status of the radio in receiving state. In this case, the high-priority services, such as short message service or call service, cannot be received by the radio in transmitting state.